System for securing covers within tanks

ABSTRACT

A system for covering liquids stored within an open-topped liquid storage tank having a peripheral wall has a cover for extending across at least a portion of stored liquids, and two or more guide assemblies spaced about the peripheral wall for securing the cover to the peripheral wall and for permitting the cover to freely travel substantially vertically up and down within the interior space. Each assembly has a vertical guide, a clamping member, and an upper and a lower delimiting stop. The cover can be operatively secured to the assembly by a restraining tether.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefits under 35 U.S.C 119(e) of the U.S. Provisional Application Ser. No. 61/738,643, filed on Dec. 18, 2012, the subject matter of which is incorporated fully herein by reference.

FIELD

Embodiments described herein generally relate to covers for covering liquids in an open top tank containing liquids, and more particularly, an apparatus for securing the cover to the open top tank.

BACKGROUND

Some industrial processes, including hydraulic fracturing (fracking) of subterranean formations, require large amounts of liquids to be temporarily stored in large, open-top portable tanks on-site in remote locations. The liquids, most often water, cannot be allowed to freeze. In cold climates, the portable tanks used in these applications are heated. To increase the efficiency of the heating process, insulated tank covers are often used, however difficult they may be to handle.

Often the walls forming the portable tanks are structurally insufficient to support large loads imposed by large tank covers. Furthermore, snow and rain deposits on the tank covers can cause stretching of the covers.

Further, in situations where there are high winds, the wind can catch open or unsecured edges of the tank cover and cause relocation or bunching of the cover. High winds or convection fluid currents in the tank can also cause water turbulence resulting in the breaking of adhesion between the cover and liquids, exacerbating problems with bunching and other wind related concerns.

Finally, snow or rain laden tank covers are often difficult to remove from the tank left resting on or adjacent the bottom of the tank when the tank is substantially empty, thereby making it very difficult to drain any remaining liquid remnants from the bottom of the tank.

There remains a need for a tank cover for portable frac fluid tanks that is versatile and tolerant of environmental conditions.

SUMMARY

An assembly is provided for securing tank covers within an interior space of an open-topped liquid storage tank. The tank comprises a peripheral wall having two or more assemblies spaced thereabout, the cover having a generally planer portion extending across a least a portion of the tank and being secured between the assemblies. Each assembly is a cover support comprising a substantially vertical guide and a clamping member at a top end thereof for securing the guide adjacent the peripheral wall within the interior space of the tank. The cover is supported between assemblies via restraining tethers.

In embodiments, each restraining tether is permitted to freely travel up and down along its respective vertical guide. The cover can travel up and down while the generally planer portion remains substantially parallel to a liquid surface. A buoyant cover will therefore float in the liquid or upon the liquid surface and reposition vertically corresponding to a depth of a liquid stored within the interior space of the tank. The vertical movement can be delimited, subject to any vertical travel limits imposed by stops along the vertical guide.

The provided embodiments allow for tanks to use covers such as a flexible covers, rigid plastic, or semi-rigid covers. The covers can have a ridged perimeter such as polyvinyl chloride (PVC) pipe and having a flexible material extending therebetween. The covers overcome problems experienced in practice including periodic exposure to snow and rain load, liquid movement including turbulence, wind interference, plus stretching and reusability of the covers. The provided embodiments may also be used for either temporary or long term storage, as well as in the case of environmental applications such as securing wildlife netting to a tank. Floating covers used with this system can also have drainage holes for draining liquid away from the surface of the cover.

In a broad aspect, a system for covering liquids stored within an open-topped liquid storage tank is provided, the tank having a peripheral wall defining an interior space, a cover extending across at least a portion of the liquid; and two or more assemblies spaced about the peripheral wall for securing the cover therebetween. Each of the two or more assemblies secure the cover laterally yet permit the cover to freely travel up and down thereon. In the case of a buoyant cover, the cover can float within or on the liquid, moving up and down corresponding to a depth of the stored liquids.

In another broad aspect, an assembly for securing at least a portion of a cover within an interior space of the open-topped liquid storage tank is provided. The assembly has a vertical guide having a top end and a bottom end, a clamping member connected adjacent the top end for securing the vertical guide to the peripheral wall within the interior space of the tank, an upper delimiting stop along the vertical guide, and a lower delimiting stop along the vertical guide, wherein the cover being secured for vertical movement between the upper and lower delimiting stops.

In another broad aspect, a method for securing a cover to an open-topped liquid storage tank having a peripheral wall defining an interior space involves providing a cover for covering liquids stored within the tank, providing two or more assemblies for securing the cover therebetween, each assembly having a vertical guide, a clamping member and upper and lower delimiting stops, securing the two or more assemblies along the peripheral wall and adjacent thereto, within the interior space of the tank, securing the cover to the two or more assemblies, adjusting the upper delimiting stop to retain the cover at a maximum elevation; and adjusting the lower delimiting stop to retain the cover at a minimum elevation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view of a tank filled with liquid, having a system including a buoyant cover for covering the liquids stored therein;

FIG. 1B is a side view of a tank filled with liquid, having a system including a buoyant cover submerged in the stored liquids;

FIG. 2 is a plan view of the embodiment according to FIG. 1A, the system having four assemblies for securing a cover extending across the tank;

FIG. 3A is a perspective view of a form of assembly for securing a cover to a peripheral wall of an open-topped liquid storage tank, the assembly having vertical guide with flow passages therethrough and a tank clamping member;

FIG. 3B is a partial perspective, cross-sectional view of a form of assembly for securing a cover to a peripheral wall of an open-topped liquid storage tank, a partial view of a one edge or periphery of a cover shown tethered to a corresponding vertical guide, the guide being clamped to a portion of the top edge of the peripheral wall of the tank;

FIG. 4 is a partial side view of the assembly of FIG. 1A securing a cover in a tank that is substantially empty;

FIG. 5 is a side view of an alternate system for covering liquids stored in a frac tank wherein the assembly are not adjustable; and

FIG. 6 is a perspective view of a tank having a portion of the peripheral wall omitted for viewing the liquid and submerged portion of a cover therein, the cover comprising two or more sections, each section being independently adjustable and of varying depth in the liquid.

DETAILED DESCRIPTION

With reference to FIGS. 1A and 1B, a system is provided for managing liquids stored within an interior space of an open-topped storage tank. The system is scalable to enable use of a cover on an open-topped liquid storage tank of any size or shape for securing a cover over, or submerged within, liquids stored within the tank.

As shown, an open-topped tank 10 is defined by a peripheral wall 15. In embodiments, the tank 10 is cylindrical having a circular peripheral wall 15, or can comprise a plurality of segments to form a circular or polygonal-shaped wall.

A cover 20 is placed within the interior space of the tank 10. The cover 20 has a generally planer portion extending across the tank 10. The cover 20 can be buoyant, having a pre-determined buoyancy for floating upon or at a depth within the liquid L. As shown in FIG. 1A, the cover 20 is a floating cover 20 capable of floating on top of the liquids L stored in the tank 10. As shown in FIG. 1B, the cover 20 is a buoyant cover that may reside submerged within the liquid or may float upon the liquid if not otherwise constrained.

The cover 20 is secured across the interior space of the tank 10 and adjacent to the peripheral wall 15 by two or more guide assemblies 25,25 spaced about the peripheral wall 15. The guide assemblies 25,25 guide the cover 20 up and down within the tank 10 as determined by liquid depth D, constraints set by the assemblies, or both. In the case of the cover of FIG. 1A, the cover 20 floats on the surface of the stored liquids and moves up and down corresponding to, or in synchronicity, the depth D of the liquids L stored within the tank 10 and may have an upper extent or maximum elevation and a lower extend or minimum elevation constrained by the assemblies themselves. As shown in FIG. 1B, the cover 20 is shown submerged; either being constrained below the surface of the liquid L or having a pre-determined buoyancy for a general equilibrium in a submerged state.

With reference to the plan view of FIG. 2, the number of assemblies 25 can vary depending on the geometry of the tank 10 and a desired number of secure connection points spaced about the peripheral wall 15 to secure the cover 20 across the tank 10. As shown, four guide assemblies 25 a,25 b,25 c,25 d are spaced circumferentially about the tank 10, generally equidistant from one another, at about quadrants of the cover 20. An effective quantity and spacing of the assemblies 25,25 is achieved when the cover 20 is able to hold its disc-like shape, achieving the desired coverage of the liquid surface area, without a periphery of the cover 20 breaking contact with the liquids, even under turbulent and windy conditions. For example, while two assemblies can provide structure for a cover that itself has structure, three assemblies can provide support for a cover that itself has no structure

For example, and as shown, a circular open-topped tank 10 is shown to have four assemblies 25 a,25 b,25 c,25 d, positioned equidistant from one another along the peripheral wall 15. To minimize a load placed on any one of the four assemblies 25 a,25 b,25 c,25 d, assemblies 25 a,25 c are positioned opposite one another and assemblies 25 b,25 d are positioned opposite one another as well. However, a skilled person would understand that increasing the number of assemblies used to secure a cover 20 to the tank 10 will clearly reduce the load placed any one assembly 25.

With reference to FIGS. 3A and 3B, each assembly 25 comprises an elongate vertical guide 30 having a top end 35 and a bottom end 40. The guide 30 can be tubular or a rod having a generally unadorned and unimpeded section therealong for enabling movement of the cover 20 therealong as described below. A clamping member 45, such as a C-clamp, is supportably connected adjacent the top end 35 for securing the assembly 25 to the peripheral wall 15 with the guide oriented substantially vertically in the tank 10. Each clamp 45 can be fit with dampeners 100 disposed between the clamping assembly 45 and the peripheral wall 15 for reducing the adverse effect of loads on the assembly 25 being imposed on the wall 15.

As shown, in FIG. 3B, the clamping member 45 can comprise a lateral extension 70 for spacing the vertical guide 30 radially towards and away from the peripheral wall 15. The lateral extension 70 can also be laterally adjustable and the guide 30 can be vertically adjustable.

A restraining tether 50 is secured at a first end to the cover 20 and connected at a second end to the assembly 25 such as by a connector or ring 55. The connector or ring 55 is disposed about the guide 30 for travel up and down the guide 30, thereby permitting the cover 20 to also travel up and down. The restraining tether 50 is moveably secured to the vertical guide 30 by a connector including the illustrated ring 55. The restraining tether 50 can be a chain, cable, rope or other tensile connecting means.

Although not shown, a person of ordinary skill in the art would understand that the tether 50 can be secured to the cover 20 at the first end using a variety of known including grommets, clamps or other connecting loops or hooks.

The cover 20 is secured between the two or more assemblies 25,25 while permitting free vertical displacement of the cover while minimizing lateral and twisting movement of the cover 20. By adjusting the length of the restraining tether 50, an operator can ensure that the cover 20 is relaxed or is pulled taut so as remain laterally in place, in contact with the surface of the liquid, even in windy conditions, thus only permitting vertical movement of the cover 20, in response to the changing depth of the stored liquids.

In an embodiment, and as shown in FIGS. 1A and 1B, edges 22 of the cover 20 can be partially submerged to ensure that water surface tension aids in consistently retaining the cover 20 in contact with the surface of the stored liquids L, even under windy or turbulent conditions.

With reference in particular to FIGS. 1B, 3B, and 4, in order to constrain or limit the range of travel of the floating cover 20 the range of movement of the restraining tether 50 on the guide 30 can be delimited. In an embodiment, the range of movement is limited to ensure that edges 22 of the cover 20 remain in contact with the surface of the stored liquids and no higher, or to maintaining the cover 20 at or about the bottom of the tank 10 when empty.

Accordingly, and in an embodiment, the guide 30 can have an adjustable upper delimiting stop 60, normally positioned towards or adjacent the top end 35, adjustably moveable along the vertical guide 30 for positioning or retaining the cover 20 at a maximum elevation. Similarly, an adjustable lower delimiting stop 65, normally positioned towards or adjacent the bottom end 45, is also adjustably moveable along the vertical guide 30 for retaining the cover 20 at a minimum elevation. The lower delimiting stop 65 further ensures that the ring 55, and connected restraining tether 50, remains disposed about the vertical guide 30, and does not fall off or otherwise disengage from the vertical guide 30.

Referring back to FIGS. 1A and 1B, the upper delimiting stop 60 can be set at an upper limit for when the tank is holding liquids at a design depth D. Being aware of a length of the restraining tether 50, an operator can adjust the upper extent or maximum elevation of the upper delimiting stop 60 such that edge 22 of the cover 20 can be positioned to be floating on the surface of the liquids stored or alternatively, as shown in FIG. 1A, the edge 22 of the cover 20 can be positioned to be partially submerged under the liquid surface for maintaining contact with the surface of the stored liquid, minimizing risk of wind being able to lift the cover 20, or as shown in FIG. 1B, the entire cover 20 is submerged.

With reference to FIG. 4, when the depth of the stored liquids decrease and when the cover 20 moved down the guides 30, the ring 55 and restraining tether 50 can engage and be supported upon the lower delimiting stop 65 with the cover 20 adjacent or on a bottom surface 75 of the tank 10.

In one embodiment, the lower stop 65 can be positioned at a lower extent or minimum elevation to allow the tether 50 and the edges of the cover 20, to be spaced away and elevated from the bottom surface 75 of the tank 10 for providing clearance for drainage hoses and for ease of lifting and removing the cover 20 when the tank 10 in substantially empty of liquids.

The upper and lower stops 60,65 on each assembly 25 can be fixed or adjustable along the guide 30 through manual or automated means. The system enables accommodation of liquids L at any depth D required in the tank 10 as well as any desired clearance between the bottom surface 75 of the tank 10 and the edges 22 of the cover 20 when the tank 10 is emptied.

The ability of the system to allow the cover 20 to freely travel substantially vertically, corresponding to the depth D of the liquids stored in the tank 10, further prevents stretching of the cover 20 under the weight of snow or rain collected thereon, as compared to prior art systems that secure the cover by means where the cover remains suspended, wholly elevated after the liquids L are removed from the tank 10.

As discussed earlier, it is common to apply heat to the tank 10 prevent avoid of the stored liquids L. As a result, there can be instances of convection currents forming within the liquids. Consequently, convection currents can cause movement or even turbulence in the stored liquids which can apply lateral or rotational loads on the guides 30. In some instances, lateral or rotational loads on the guides 30 can be imparted to the peripheral walls 15 by the clamping members 45, increasing the potential for the assembly 20 to disengage from the peripheral wall 15, or even twist or bend the vertical guide 30.

Accordingly, and referring back to FIG. 3A, the guide 30 can be rendered less susceptible to liquid currents by including plurality of openings 80 extending laterally through the vertical guides 30. The plurality of openings 80 can be spaced apart along the length of the vertical guide 30 and permit liquid to pass through the vertical guides 30, thereby reducing the load placed thereon. The quantity and size of the openings 80 can be dependent on the material strength of the guide 30. Depending on prevailing currents, the cross-section of the vertical guide 30 can also be airfoil-shaped (not shown), for reducing a surface area exposed to horizontal forces of the convection currents within the tank 10. The reduced surface area of the vertical guide 30 allows for a reduction in stresses exerted thereon, helping reduce bending and torsional forces on the peripheral wall 15 of the tank 10. Although not shown, in embodiments, any remaining torque can be reduced through shock dampers provided on the contacting surfaces of the clamping member 45.

With reference to FIG. 5 and in another embodiment, the system can comprise a floating cover 20 and two or more weights 85,85 for anchoring the cover 20 within the tank 10. Each of two or more tethers 90,90 secures a portion of the cover 20 to the two or more weights 85,85. The upper extent or maximum elevation of the movement of the cover 20 is controlled by the length of the tether 90 and the lower extent or minimum elevation of the cover 20 is controlled by the height or positioning of the two or more weights 85,85. As the liquid contents of the tank 10 are removed, the cover 20 travels toward the bottom surface 75 of the tank 10. The two or more weights 85,85 can be positioned below the perimeter or edge 22, or radially inboard below the cover 20, to also act as a stop for the cover 10, elevating at least the perimeter of the cover 10 from the bottom surface 75 of the tank and preventing it from resting on the bottom surface 75.

In an embodiment, the cover 20 can be a floating or buoyant cover, an insulated cover, a membrane cover having a floating perimeter, flexible covers, rigid or semi-rigid covers, covers having a ridged perimeter such as polyvinyl chloride (PVC) pipe and flexible material extending therebetween, or the like. Otherwise, the cover can be a membrane or structure that is substantially supported at its periphery at tethers to assemblies 25. Although not shown, cover 20 can have drainage holes for draining liquid away from the surface of the cover.

With reference to FIG. 6, in another embodiment, the floating cover 20 can have two more or sections 20 a,20 b. Each section 20 a and 20 b can be secured to the tank 10 by its corresponding assemblies 25,25, permitting each section 20 a,20 b to freely move up and down with a changing of the depth of the stored liquids L, independent of any other section or by adjusting a buoyancy characteristic and/or the upper limit for each section 20 a or 20 b (independent of any other section), each section 20 a or 20 b can be caused to be positioned within the stored liquids at varying heights or depths. As shown, section 20 a can be floating on the surface of the stored liquids L while section 20 b is submerged in the stored liquids L, effectively creating topside access 95 to the stored liquids L and possibly providing a baffling effect, altering the pattern of the convection currents within the stored liquids L. The sections 20 a,20 b can be tethered together with flexible connectors. 

The embodiments of the invention for which an exclusive property or privilege is claimed are defined as follows:
 1. A system for covering liquids stored within an open-topped liquid storage tank having a peripheral wall defining an interior space comprising: a cover extending across at least a portion of the liquid; and two or more assemblies spaced about the peripheral wall for securing the cover therebetween, wherein each of the two or more assemblies permit the cover to freely travel substantially vertically up and down within the interior space.
 2. The system of claim 1, wherein each of the two or more assemblies further comprises: a vertical guide having a top end and a bottom end; a clamping member connected adjacent the top end for securing the vertical guide to the peripheral wall within the interior space of the tank; an upper delimiting stop along the vertical guide; and a lower delimiting stop along the vertical guide, wherein the cover being secured for vertical movement between the upper and lower delimiting stops.
 3. The system of claim 1, wherein the cover is buoyant and moves up and down corresponding with a depth of the liquid.
 4. The system of claim 1, further comprising: a restraining tether between each of the two or more assemblies and the cover for securing the cover across the interior space of the tank, the restraining tether freely moveable along the vertical guide and disposed between the upper and lower delimiting stops.
 5. The system of claim 4, wherein the restraining tether is secured to the cover at a first end and connected to the vertical guide at a second end, the second end comprising a ring moveable along the vertical guide.
 6. The system of claim 5, wherein the tether is secured to the cover at the first end using grommets.
 7. The system of claim 2, wherein the upper delimiting stops are positioned to retain the cover at a maximum elevation.
 8. The system of claim 2, wherein the lower delimiting stops are positioned to retain the cover at a minimum elevation.
 9. The system of claim 2, wherein the position of the upper and lower delimiting stops is automated.
 10. The system of claim 2, wherein the clamping member further comprises a lateral extension for spacing the vertical guide radially to and from the peripheral wall.
 11. The system of claim 2, wherein the vertical guide further comprises a plurality of openings therethrough for permitting liquids to travel therethrough.
 12. An assembly for securing at least a portion of a cover within an interior space of an open top liquid storage tank having a peripheral wall defining the interior space of the tank, comprising: a vertical guide having a top end and a bottom end; a clamping member connected adjacent the top end for securing the vertical guide to the peripheral wall within the interior space of the tank; an upper delimiting stop along the vertical guide; and a lower delimiting stop along the vertical guide, wherein the cover being secured for vertical movement between the upper and lower delimiting stops.
 13. The assembly of claim 12, further comprising: a restraining tether between the assembly and the cover for securing the cover across the interior space of the tank, the restraining tether freely moveable along the vertical guide and disposed between the upper and lower delimiting stops.
 14. The system of claim 12, wherein the restraining tether is secured to the cover at a first end and connected to the vertical guide at a second end, the second end comprising a ring moveable along the vertical guide.
 15. The assembly of claim 12, wherein the upper delimiting stops are positioned to retain the cover at a maximum elevation.
 16. The assembly of claim 12, wherein the lower delimiting stops are positioned to retain the cover at a minimum elevation.
 17. The assembly of claim 12, wherein the position of the upper and lower delimiting stops are automated.
 18. The assembly of claim 12, wherein the clamping member further comprises a lateral extension for spacing the vertical guide radially to and from the peripheral wall.
 19. The assembly of claim 12, wherein the vertical guide further comprises a plurality of openings therethrough for permitting liquids to travel therethrough.
 20. A method for securing a cover to an open-topped liquid storage tank having a peripheral wall defining an interior space comprising: providing a cover for covering liquids stored within the tank; providing two or more assemblies for securing the cover therebetween, each assembly having a vertical guide, and upper and lower delimiting stops; securing the two or more assemblies along the peripheral wall and adjacent thereto, within the interior space of the tank; securing the cover to the two or more assemblies for up and down movement along the vertical guides; adjusting the upper delimiting stop to retain the cover at a maximum elevation; and adjusting the lower delimiting stop to retain the cover at a minimum elevation. 